The invention described herein relates generally to a turbine airfoil assembly. More specifically, the invention relates to a turbine airfoil assembly configured for improved cooling performance.
Turbine airfoil assemblies direct gaseous flow passing through rotor assemblies within a gas turbine. For example, a stator vane assembly may include one or more stator vane airfoils extending radially between an inner and an outer platform. The temperature of core gas flow passing the stator vane airfoil typically requires cooling within the stator vane, and this cooling helps to increase stator vane life.
In many gas turbines, some components must be cooled to extend operating life. Cooling air at a lower temperature and higher pressure than the core gas is typically introduced into an internal cavity of a stator vane, where it absorbs thermal energy. The cooling air subsequently exits the vane via apertures in the vane walls, transporting the thermal energy away from the vane. The pressure difference across the vane walls and the flow rate at which the cooling air exits the vane is important, particularly along the leading edge where temperatures may be elevated. In the past, internal vane structures have been defined by first establishing the minimum acceptable pressure difference at any point along the leading edge (internal versus external pressure), and subsequently manipulating the internal vane structure along the entire leading edge such that the minimal allowable pressure difference is present along the entire leading edge. The problem with this approach is that core gas flow pressure gradients along the leading edge of a vane may have one or more small regions (i.e., “spikes”) at a pressure considerably higher than the rest of the gradient along the leading edge. This is particularly true for those stator vanes disposed aft of rotor assemblies, where relative motion between rotor blades and stator vanes can significantly influence the core gas flow profile. Increasing the minimum allowable pressure to accommodate the spikes consumes an excessive amount of cooling air.
Prior approaches have modified the internal vane structure, but this approach does not permit customization. Turbines may be installed in a wide variety of locations (e.g., hot, cold, dry, humid, etc.) and the same turbine in a very cold and humid environment may experience a very different core gas flow pressure gradient than a turbine installed in a hot and dry environment.